Strongylidium koreanum, Chae & Park & Min, 2023

Chae, Kyu-Seok, Park, Kyung-Min & Min, Gi-Sik, 2023, Strongylidium koreanum n. sp. (Protozoa: Ciliophora), a new soil species from South Korea, Zootaxa 5227 (2), pp. 194-204 : 199-202

Comparison of S. koreanum n. sp. with morphologically related species

In the comprehensive revision of Strongylidium by Paiva & Silva-Neto (2007), Strongylidium spp. were divided into five groups. Group I is characterized by two long ventral and two marginal cirral rows, which includes the type species S. crassum Sterki, 1878 . To date, 17 species have been assigned to group I, and S. koreanum n. sp. was found to belong to this group. S. koreanum n. sp. should be compared with S. orientale , S. pseudocrassum , S. contortus , and S. crassum , considering its two macronuclear nodules and position of the contractile vacuole ( Table 2).

Strongylidium orientale is highly similar to S. koreanum n. sp. in the number of adoral membranelles and the left ventral, left, and right marginal cirri. By contrast, both differ from anterior end of the right ventral cirri (above the proximal end of the adoral zone of membranelles vs. below), cortical granules (present vs. absent) and habitat (brackish water vs. terrestrial) ( Chen et al. 2013).

Strongylidium pseudocrassum can be distinguished from S. koreanum n. sp. by its macronuclear nodules (2–4 vs. 2), distance from the anterior edge of the cell to the anterior end of the right ventral cirral row (9–26 µm vs. 37–45 µm), anterior end of the right ventral cirri (above the proximal end of the adoral zone of membranelles vs. below), cortical granules (present vs. absent) and habitat (freshwater vs. terrestrial) ( Paiva & Silva-Neto 2007).

The data for S. contortus were insufficient because of the absence of a staining method. Thus, the characteristics seen in the illustrations were used. Strongylidium contortus differs from S. koreanum n. sp. in the number of right (ca. 46 based on the figure vs. 15–28, mean 21) ventral cirri, anterior end of right ventral cirri (above proximal end of adoral zone of membranelles vs. below), and habitat (freshwater vs. terrestrial) ( Gelei 1954).

Strongylidium crassum can be separated from S. koreanum n. sp. by the absence of a postoral ventral cirrus (vs. present), anterior end of right ventral cirri (above proximal end of adoral zone of membranelles vs. below), and single micronuclei located between two macronuclear nodules (vs. 2) ( Kahl 1932).